help for curved plate steel bridge needed

Don't.
Use straight spans between piers, the spans may need to be wider than normal.
The prototype use straight spans between piers. Curved spans or spans consisting of short straight sections don't work. They would tumble to the earth when the first train passed over them.

You do short straight sections that are wider than the track width. The easiest way to do this (providing that you aren't going to look up the skirts of the bridge) is to just lay your subroadbed just wide enough for the track and come back again with bridge sides that are in the 50'-100' lengths and cover the sides of the subroadbed followed by the filling in of the gaps with ballast to the girder bridge sides. Needless to say, each joint in the bridge segments needs to have it's own pier to support the two ends of the two girder segments. You can either make the two sides of the girder different lengths or the same length, depending upon how you feel. The different length is the more correct construction but the equal length has also been done.
-- Why do penguins walk so far to get to their nesting grounds?

If you wanted to do a curved bridge, it would have to be a masonry (brick or stone) one. For all other materials, a series of tangents would have to be used. Regards, Bill.

That's funny... because in the past you wrote "Of course it [curved plate girders for railroad bridges] can be done..." ____ Mark

It's funny that you don't cite the whole message:
"Of course it can be done but not without consideration to the stability problems that arise, and the curved spans have to be short in any case. Normally curved girders are considered bad engineering practice, and it is more cost effective to use short straight spans."
The first post in this thread was talking about bridges with steel plate girders:
"I am in need of details to make a curved bridge.
the radius is 30". & I am wanting to use a steel plate type bridge set on piers. the spans will be approx scale 40' between piers, with 4 spans over all."
As for steel and concrete box girders these types have much larger torsional strenght and stiffness, thus the practical possibility of making curved girders of this design is much better.
As for steel plate girders, curved girders is still in my opinion "bad engineering practice".

The link supplied had the whole massage! Didn't you look at it?

If you read my message you wouldn't have reason to ask.

I did read your whole message; the link I included cited the WHOLE message. How can you even try to claim that I didn't cite the whole message?
Here's the citation I used: ____ Mark